Sorry you didn't get any takers on this one, Rick - surprising! OK, I'll throw in my 2 cents worth...
Beef tenderloins are filet mignon, right? So, you probably want a medium-rare finish? If that's the case, you might consider my prime rib method. Season them, then slow cook at 200 to an internal temp of 128. Wrap them, and bring the grill up to 500. Then, reverse-sear on the hot grill to cook the surface. If they only spend 5-7 minutes total on the grill, you shouldn't overcook the inside.
Although you have conventional thinking in your plan, tenderloins are not that big. I think grilling first, and then using the 300-degree smoker will cook them outside-in, and will result in overcooked loins. You want to cook them slowly from the inside out, then finish the surface, in my opinion.
Good luck, whichever way you go, and Merry Christmas!
